1. FIELD OF THE INVENTION
The present invention relates to dobbies and other weaving mechanisms used for forming the shed in weaving looms, and more particularly to the control of these mechanisms by electro-magnetic means.
2. HISTORY OF THE RELATED ART
It is known that, in order to simplify the construction of dobbies, it has been proposed to replace the conventional reading apparatus employing punched paper, punched cards or pegged cylinder, by electromagnetic systems comprising two series of electromagnets placed under the control of a memory containing the weaving program corresponding to the weave desired for the fabric being produced on the loom. One of these series of electro-magnets corresponds to normal operation, the other to reverse operation or "unweaving". Each of them contains a number of electro-magnets equal to that of the independent actuation devices of the dobby or other mechanism, i.e. to the number of the heddle frames mounted on loom.
In the known constructions, each electro-magnet comprises a coil for attracting, against elastic return means, a pivoting blade of which the free end is adapted, in one of the two positions of operation, to form a stop for a needle displaced reciprocally along its axis. The needle cooperates with a device equipped with pushers and knives which reciprocate in order to effect control of an actuation lever of the dobby.
It will be readily appreciated that such a structure involves a complex assembly which, if it is desired to obtain faultless operation at the high speeds of weaving which are now adopted, must necessarily be very precise since any error in positioning necessarily creates a risk of defective functioning.
In practice, in order to compensate for the imprecisions resulting from the complexity of construction, the clearance of the blades or other mobile armatures is increased, which is detrimen-mobile to performance and requires more electrical power, causing overheating and leading to a higher cost.
It is an object of the present invention to overcome these drawbacks by providing an electro-magnetic control unit which presents a simplified structure ensuring fault-free operation.